一种平衡式环行器收发隔离电路的设计与实现

A TX and RX Isolation Circuit with Balanced Circulators

对于收发天线一体、收发频率相近、收发信号同时存在的无线电通信应用场景,比如UHF RFID的读卡器,目前一般使用单独的环行器来进行收发隔离,但其隔离度有限,一般在20 dB左右。从理论上分析了由两个环行器组成的平衡式环行器隔离电路的隔离原理,并提出了一种改进平衡式环行器收发隔离电路,同时制作了电路模块。网络分析仪测试表明,该改进平衡式环行器收发隔离电路的发射端到天线端的传输损耗和天线端到接收端的传输损耗都在1 dB以内,在连接驻波比为1.2∶1的板式天线情况下,其收发隔离度达到了50 dB以上;实测当射频输入功率处于0.1 W~8.0 W区间时,该电路的收发隔离度稳定在40 dB以上,较使用单独环行器时的隔离度至少提高了20 dB。

The transmitting-and-receiving isolation technology is the key point for the application scenarios of the transceiver such as the UHF RFID reader with common antenna, similar TX and RX frequency and simultaneous occurrence of TX and RX signals. At present, a separate circulator is generally used for the above-mentioned application, but its TX to RX isolation is just about 20 dB. The principle of balanced circulator is analyzed theoretically, and an improved balanced circulator isolation circuit is proposed. This module’s testing results show that the transmission loss from the TX to the antenna port and the transmission loss from the antenna port to the RX are both within 1 dB,this module’s TX to RX isolation has reached more than 50 dB when an antenna with 1.2∶1 VSWR is connected. When the radio frequency power of the TX signal ranges within 0.1 W to 8.0 W,the isolation has stayed stably above 40 dB,at least 20 dB higher than that of a separate circulator.